The overall goal of this project is to identify and characterize intermediate calcium carriers which have a common mineralizing function in distantly related organism and to determine how carrier-bound calcium ions are utilized to form a crystalline mineral phase. As a working hypothesis, it is proposed that polyanionic macromolecules function as intermediate calcium carriers, i.e. that polyanions are charged with mineral ions intracellularly and are subsequently degraded at calcifying foci releasing mineral ions for crystal growth. The specific aims are designed to test the carrier hypothesis in two homogeneous cell populations and in a complex metazoan tissue. The first aim is to identify and characterize the calcium-binding polyuronides that are apparently degraded at the mineralization front in coccolithophorid algae. The kinetics of polyuronide turnover will be analyzed to determine if there is a one-to-one correspondence between the number of calcium ions released via the degradation of these polyanions and the number of calcium ions deposited in the mineral phase. The second aim is to determine whether the spicule-forming primary mesenchyme cells derived from sea urchin embryos express a polyanionic calcium-binding phosphoprotein(s). If a protein with these properties is expressed, its calcium-binding capacity and rate of turnover will be analyzed in relation to the rate of calcium deposition in the spicules. The third aim is to examine the self-association of a bone phosphoprotein osteopontin in the presence of calcium, magnesium and phosphate ions. The purpose of this study is to determine whether osteopontin forms discrete aggregates containing sequestered Ca3 (PO4)2-like complexes similar to known calcium- carriers, e.g. casein. The fourth aim is to examine the distribution of phosphoproteins in the matrix of embryonic chick calvaria to determine whether matrix phosphoprotein is preferentially concentrated at mineralizing foci. This project is relevant to normal skeletal and pathological calcification processes.